Step 1
Find a single-breasted trench coat — a double-breasted coat will draw even more attention to your chest, which you don't need — with long, fitted sleeves and that falls to mid-thigh to elongate your body.
Step 2
Get a trench with a waistbelt to help define your waist.
Step 3
Wear the trench buttoned up all the way, or leave a couple of buttons at the top undone. The farther up your coat you button, the longer and leaner your body appears.
Step 4
Wrap the belt around your waist snugly and tie it in place at the front, slightly off to the side. Without a belt around your waist, a large chest would make your body look larger than you actually are, because there isn't any definition between your chest and waist.